This invention relates to functional polyolefiln material that contains a terminal phenyl or substituted phenyl group, and to a process for its preparation. More particularly, this invention relates to a functional polymer having a polyolefin polymer backbone that is a homopolymer or copolymer prepared by metallocene coordination polymerization of linear, branched or cyclic C3-C18 alpha-olefins and/or diolefins, in which the molecular weight of polyolefin backbone is above about 500 g/mole, preferably from about 10,000 to 1,000,000 g/mole. The process by which the functional polymer material is prepared involves a novel sequential chain transfer reaction, first to styrene (or a styrene derivative) and then hydrogen, during the transition metal mediated olefin polymerization, to produce polyolefin having a terminal phenyl or substituted phenyl group.
Although useful in many commercial applications, polyolefins suffer a major deficiency, i.e., poor interaction with other materials. The inert nature of polyolefins significantly limits their end uses, particularly those in which adhesion, dyeability, paintability, printability or compatibility with other functional polymers is paramount. Polymers containing a terminal functional group are particularly desirable materials. For example, they can be used as interfacial agents during reactive extrusion processes to improve adhesion and compatibility in polymer blends and composites. Polymers containing a terminal functional group also can serve as reactive building blocks for the preparation of block and graft copolymers.
In general, the chemistry for introducing a functional group to the chain end of a vinyl polymer is very limited. Usually, these polymers are prepared by terminating living polymers with suitable reagents. The anionic, cationic, and metathesis living polymerizations are particularly preferred because they provide a stable propagating active site that can be converted effectively to the desired functional group at the polymer chain end. [For examples of anionic living polymerization, see, e.g., U.S. Pat. No. 3,265,765 and D. E. Bergbreiter et al, J. Am. Chem. Soc., 109, 174, 1987; for cationic living polymerization, see, e.g., U.S. Pat. No. 4,946,899; and for metathesis living polymerization, see, e.g., R. H. Grubbs, et al, Macromolecules, 22, 1558, 1989]. However, a corresponding termination process in transition metal coordination polymerization of alpha-olefins is very rare due to the generally non-living nature of transition metal olefin catalysis. Only a few examples of living transition metal coordination polymerization have been reported, and those have been accomplished under very inconvenient reaction conditions and using specific catalysts [see Y. Doi, et al, Makromol. Chem., 188, 1273, 1987; Makromol. Chem., 186, 1825, 1985; Makromol. Chem. Rapid Comm., 5, 811, 1984; and H. Yasuda, et al, Macromolecules, 25, 5115, 1992].
Several years ago, a new living catalyst system, based on late transition metals, e.g., cobalt (III) complex, was reported as being useful in the preparation of functional group-terminated polyethylene [see, M. Brookhart, et al, Macromolecules, 28, 5378, 1995]. The metal complex was first reacted with a phenyl group before initiating ethylene polymerization. In other words, the functional group was introduced into the beginning of polymer chain. To prevent the deactivation of the active site, the functional group had to be blocked from the electrophilic Co (III) during the polymerization. Overall, the catalyst activity was relatively low because each catalyst active site produced only one polymer chain. In addition, the polymer structure was limited to the branched polyethylene. To date, the applicants are unaware of any late transition metal catalyst that has been shown to incorporate alpha-olefins, such as propylene and 1-butene, with isotactic insertion into an olefin polymer backbone.
Another approach toward preparing functional group terminated polyolefin was via in situ chain transfer reaction to a co-initiator during Ziegler-Natta polymerization. Several Al-alkyl co-initiators [see, U.S. Pat. No. 5,939,495] and Zn-alkyl co-initiators [sere, Shiono et al., Makromol. Chem., 193, 2751, 1992 and Makromol. Chem. Phys., 195, 3303, 1994] were found to engage chain transfer reactions to obtain Al and Zn-terminated polyolefins, respectively. The Al and Zn-terminated polyolefins can be further modified to prepare polyolefins having other terminal functional groups. However, the products comprise a complex mixture of polymers containing various end groups, due to ill-defined catalyst systems that also involve other chain transfer reactions, such as xcex2-hydride elimination and chain transfer to monomer.
Another method reported for the preparation of functional group terminated polyolefin is based on chemical modification of chain end unsaturated polypropylene (PP), which can be prepared by metallocene polymerization or thermal degradation of high molecular weight PP. [see Chung et al, Macromolecules, 32, 2525, 1999; Macromolecules, 31, 5943, 1998; Polymer, 38, 1495, 1997; Mulhaupt et al, Polymers for Advanced Technologies, 4, 439, 1993; and Shiono et al, Macromolecules, 25, 3356, 1992; Macromolecules, 26, 2085, 1993; Macromolecules, 30 5997, 1997]. The effectiveness of this chain end functionalization process is strongly dependent on (a) the percentage of polymer chains having a vinylidene terminal group and (b) the efficiency of functionalization reaction. It has been observed that the efficiency of the functionalization reaction decreases with an increase of PP molecular weight, due to the decrease of vinylidene concentration. Some functionalization reactions are very effective for low molecular weight PP. However, they become very ineffective for PP polymer having a molecular weight in excess of about 30,000 g/mole. Unfortunately, for many applications, such as for improving the interfacial interactions in PP blends and composites, a high molecular weight PP chain is essential. In addition, the availability of chain-end unsaturated polyolefins is very limited and most polyolefins, except polypropylene, have a low percentage of chain end unsaturation in their polymer chains.
In general, developments in homogeneous metallocene catalysis have provided a new era in polyolefin synthesis [see, e.g., U.S. Pat. No. 4,542,199; U.S. Pat. No. 4,530,914; U.S. Pat. No. 4,665,047; U.S. Pat. No. 4,752,597; U.S. Pat. No. 5,026,798 U.S. Pat. No. 5,272,236]. Thus, with well-designed, single-site catalysts having a constrained ligand geometry, the incorporation of higher alpha-olefins into a polymer chain has been greatly enhanced. This has significantly expanded the scope (composition and molecular structure) of polyolefin material, and has enabled the preparation of a variety of polymers having narrow molecular weight and composition distributions, including linear low density polyethylene (LLDPE), poly(ethylene-co-styrene) [see, e.g., U.S. Pat. No. 5,703,187], poly(ethylene-co-p-methylstyrene ), poly(ethylene-ter-propylene-ter-p-methylstyrene) and poly(ethylene-ter-1 -octene-ter-p-methylstyrene) [see, e.g., U.S. Pat. Nos. 5,543,484 and 5,866,659].
The narrow molecular weight and composition distributions of the metallocene-prepared polyolefins are the results of a well-defined polymerization mechanism, including initiation, propagation, termination, and chain transfer reactions. In recent years, Marks and Chung have applied the well-defined chain transfer reaction to terminate a propagating polyolefin chain with silane reagents [see Marks, T. J., J. Am. Chem. Soc., 120, 4019, 1998; J. Am. Chem. Soc., 117, 10747, 1995; Macromolecules, 32, 981, 1999] and with borane reagents [see Chung, T. C., J. Am. Chem. Soc., 121, 6764, 1999; Macromolecules, 32, 8689, 2000]. Several organosilanes having Si-H groups and several boranes having B-H groups have been shown to be effective chain transfer agents in metallocene-mediated polymerizations that result in silane-terminated and borane-terminated olefin polymers and copolymers, respectively. Hessen [Hessen et al., J. Am. Chem. Soc. 121, 6082, 1999] also studied C-H in thioplhene as a chain transfer agent in ethylene polymerization using a neutral yttrium catalyst system. In general, the polymerization was extremely sluggish with very low catalyst activity. Kim [Kim S. Y. et al, Macromolecules, 33, 1921, 2000) also observed chain a transfer reaction in the copolymerization of ethylene and alkylbenzene. Unfortunately, the polymers produced showed many terminal structures, which were associated with various modes of chain transfer reactions.
In this invention, a new reactive (functional) group-terminated polyolefin is disclosed, in which the terminal group is a phenyl or substituted phenyl group. The general molecular structure of the present (functional) group-terminated polyolefin is illustrated below: 
in which polyolefin is a homopolymer or copolymer prepared by metallocene-mediated coordination polymerization of alpha-olefins and/or diolefins, including C3-C18 monomers having linear, branched or cyclic structures, and in which the term xe2x80x9ccopolymerxe2x80x9d is meant to include polymers containing groups or units derived from two or more monomers. Thus, as used in this specification and claims, the term xe2x80x9ccopolymerxe2x80x9d is meant to include copolymers, terpolymers, tetrapolymers, etc. The molecular weight of polyolefin segment is above 500 g/mole. Preferably, the molecular weight is from about 10,000 to about 1,000,000 g/mole, and most preferably from about 30,000 to about 300,000 g/mole. The number of methylene spacer units (n) is from 0 to about 6, and preferably n is from 0 to 3. X is a group selected from H, Cl, Br, I, OH, NH2, COOR, Oxe2x80x94BR2, Oxe2x80x94SiR3, N(SiR3)2, BR2, SiR3 (where R is a C1 to C10 linear, branched, cyclic or aromatic alkyl group), CHxe2x95x90CH2, COOH, COOLi, and succinic anhydride.
The invention also relates to a polymerization process for producing olefin polymers containing a terminal phenyl or substituted phenyl group. The process involves simultaneously contacting C3-C18 alpha-olefin (or/and diolefin) monomers with styrene (or a styrene derivative) and with hydrogen under polymerization conditions in the presence of specific metallocene catalysts. Ironically, the metallocene catalysts contemplated for use in the present invention typically show poor styrene incorporation in copolymerization reactions between propylene and styrene. In many cases, the catalysts are deactivated after reacting with a styrene molecule. The deactivation of the catalyst apparently is due to the formation of a dormant active site after 2,1 -insertion of styrene. The bulky phenyl side group adjacent to the active site may form a complex with the cationic active site, which blocks propylene (or higher xcex1-olefins) 1,2-insertion. However, it has been found, quite unexpectedly, that the bulky active site reacts with hydrogen to release the polymer chain and to regenerate the active site for initiating a new polymer chain, as illustrated below: 
wherein, M is a transition metal of group IVB and VB metal, such as titanium, zirconium and haffium, which contains two bridged cyclopentadienyl or substituted cyclopentadienyl ligands having a covalent bridging group (such as silane, methyl and dimethyl groups). Axe2x88x92 is a non-coordinating compatible anion. Particularly desirable are aluminoxane (MAO) and borate, including tetra(pentafluorophenyl)borate and methyltri(pentafluorophenyl)borate. R1 is a C1-C10 alkyl group.
Overall, the polymerization process for producing polyolefin containing a terminal phenyl or substituted phenyl group resembles a sequential chain transfer reaction, first to styrene (or styrene derivative) and then to hydrogen, during the metallocene-mediated alpha-olefin polymerization. This process not only produces the polyolefin with a terminal pheniyl or substituted phenyl group, but also maintains high catalyst activity.
In accordance with the present invention, polyolefins containing a terminal phenyl or substituted phenyl group, sometimes referred to herein as polyolefins having a terminal styrene unit or styrene derivative unit, are prepared under generally conventional metallocene cation catalyzed polymerization conditions by polymerizing one or more C3-C18 olefin (or/and diolefin) monomers in the presence of both styrene (or a styrene derivative) and hydrogen as essential combined chain transfer agents, and in the further presence of herein-specified metallocene catalyst and co-catalyst systems.
It is essential to choose the metallocene catalyst, having a specific bridged cyclopentadienyl or substituted cyclopentadienyl structure, which can only react with one styrene (or styrene derivative) molecule, without further chain extension by incorporating either C3-C18 olefin or styrene (or styrene derivative) monomers. Therefore, the styrenic unit-terminated propagating polyolefin chain has the chance to react with hydrogen to complete the chain transfer reaction. To produce high yield of the styrenic unit terminated polyolefin, it is also important to choose the metallocene catalyst that shows very low undesirable chain transfer reactions to hydrogen, monomer, co-catalyst, and xcex2-hydride elimination, during the C3-C18 olefin homopolymerizations.
This invention is based largely on the understanding that the deactivation of some specific metallocene active sites by styrenic molecules during some metallocene-mediated olefin polymerizations is due to the formation of a dormant species at the active site. After 2,1-insertion of styrenic molecule, the bulky electron-rich phenyl group is immediately adjacent to the electron-deficient cationic active site. The combination of steric hindrance and acid-base complexation, between the active site and phenyl group, prevents further olefin insertion with 1,2-manner. However, this dormant site is very reactive to hydrogen, such that a hydrogenation reaction releases the polymer chain (containing a terminal styrenic unit) and also regenerates the active site for further polymerization. In other words, according the reaction mechanism described in this invention, the polymer formed has a terminal styrenic unit, and the polymer molecular weight is proportional to the [olefin]/[styrenic molecule] ratio. The overall polymerization rate maintains very high, similar to that of the reaction between only the olefin (or/and diolefin) monomers, without any styrene and hydrogen chain transfer agents being present in the reaction mass.
The reaction mechanism of forming the styrenic unit-terminated polyolefin may be further exemplified by the polymerization of propylene using rac-Me2Si[2-Me-4-Ph(Ind)]2ZrCl2/MAO catalyst system in the presence of p-methylstyrene (p-MS) and hydrogen chain transfer agents, as illustrated below: 
During the polymerization of propylene (with 1,2-insertion manner) the propagation Zrxe2x80x94C site (II) can also react with p-methylstyrene (with 2,1 -insertion manner) to form p-methylstyrene terminated polypropylene (III). The catalytic Zrxe2x80x94C site in compound (III) becomes inactive to both propylene and p-methylstyrene [see Chung et al., J. Polymer Science: Part A: Polymer Chemistry, 37, 2795, 1999] due to the combination of steric hindrance between the active site (Zrxe2x80x94C) and incoming monomer (propylene with 1,2-insertion) and the formation of complex between the adjacent phenyl group and the Zr+ ion. On the other hand, with the presence of hydrogen, the dormant Zrxe2x80x94C site (III) can react with hydrogen to form p-methylstyrene-terminated polypropylene (PP-t-p-MS) (V) and regenerate Zrxe2x80x94H species (I) that is capable of reinitiating the polymerization of propylene and, thus, continuing polymerization cycle. In other words, the ideal chain transfer reaction will not significantly effect the rate of polymerization, but will reduce the molecular weight of the resulting polymer. The molecular weight of PP-t-p-MS is almost linearly proportional to the molar ratio of [propylene]/[p-MS], and is basically independent of the molar ratio of [propylene]/[hydrogen]. Accordingly, it is clear that the chain transfer reaction with p-MS (rate constant ktr) is the dominant termination process, which competes with the propagating reaction with propylene (rate constant kp). The degree of polymerization (Xn) follows a simple comparative equation Xn=kp[propylene]/ktr[p-MS], with a chain transfer constant of ktr/kpxcx9c1/6.36.
In accordance with this invention, this sequential chain transfer reaction, first to styrene (or styrene derivative) and then hydrogen, during the metallocene-mediated olefin polymerization, can be applied to any C3-C18 olefin and diolefin monomers without causing undesirable side reactions, such as the copolymerization of olefin (or/and diolefin) with styrene (or styrene derivatives), or several direct chain transfer reactions from the propagating olefinic chain end to hydrogen, monomer or co-initiator, as well as xcex2-hydride elimination, as discussed above. The molecular weight of the styrenic unit-terminated polyolefin is basically controlled by the mole ratio of [olefinic monomer]/[styrenic molecule], and the general molecular structure of styrenic-unit-terminated polymer (polyolefin containing a terminal phenyl or substituted phenyl group) is illustrated below: 
wherein polyolefin is a homopolymer or copolymer prepared by metallocene-mediated coordination polymerization of linear, branched or cyclic C3-C18 alpha-olefins and/or diolefins. The molecular weight of polyolefin segment is above 500 g/mole, preferably from about 10,000 to about 1,000,000 g/mole, and most preferably from about 30,000 to about 300,000 g/mole. The number of methylene spacer units (n) is 0 and about 6, and preferably n is 0 to 3. Xxe2x80x2 is a group selected from H, Cl, Br, I, COOR, Oxe2x80x94BR2, Oxe2x80x94SiR3, N(SiR3)2, BR2, SiR3 (where R is a C1 to C10 linear, branched, cyclic or aromatic alkyl group) and CHxe2x95x90CH2.
As used in this specification and claims, the term xe2x80x9caliphatic alkyl groupxe2x80x9d is meant to include C1 to C10 linear, branched or cyclic aliphatic groups such as xe2x80x94CH2CH(CH3)CH3, xe2x80x94CH3, xe2x80x94CH2CH3 and the like. The term xe2x80x9caromatic alkyl groupxe2x80x9d is meant to include groups such as "PHgr"(Rxe2x80x2)y, where "PHgr" is phenyl, Rxe2x80x2 is C1 to C5 linear or branched alkyl, and y is 1, 2 or 3, and preferably 1. Preferred examples of "PHgr"(Rxe2x80x2)y, include "PHgr"-CH3 and "PHgr"-CH2CH3 (where "PHgr" is phenyl).
The metallocene catalysts capable of producing the present styrenic group-terminated polyolefin, via olefin polymerization-chain transfer reaction to styrene/hydrogen, is the one having minimum copolymerization capability between olefinic and styrenic monomers and showing very low direct chain transfer reaction between the propagating olefinic polymer chain end and hydrogen. Suitable catalysts, which typically produce a homopolymer having a very high molecular weight, may be illustrated by the following formula: 
where M is a transition metal of group III and IV of the Periodic Table of the Elements, L and Lxe2x80x2, independently, are cyclopentadienyl or substituted cyclopentadienyl groups bound in an xcex75 bonding mode to metal, Y is a moiety selected from xe2x80x94SiRxe2x80x22xe2x80x94, xe2x80x94CRxe2x80x22xe2x80x94, and xe2x80x94CRxe2x80x22xe2x80x94CRxe2x80x22xe2x80x94, where each Rxe2x80x2, independently, is selected from the group consisting of hydrogen, alkyl, aryl, silyl, halogenated alkyl, halogenated aryl, and mixtures thereof, Z is selected from hydride, halo, alkyl, aryl, aryloxy, and alkoxy, m is 0 or 1, and Axe2x88x92 is a non-coordinating, compatible anion derived from, for example, an aluminoxane, such as methylaluminoxane (MAO), or a borate, such as tetra(pentafluorophenyl)borate and methyltri(pentafluorophenyl)borate.
One known method of making the ionic catalyst species useful in this invention involves combining (a) a transition metal compound and (b) a compound capable of reacting with a transition metal compound to form an ionic complex. In the reaction of compounds (a) and (b), the compound (a) forms a cation formally having a coordination number that is one less than its valence, and the compound (b) becomes a non-coordinating, compatible anion. The amount of such transition metal compound employed generally will range from about 20 ppm to about 1 wt. %, and preferably from about 0.001 to about 0.2 wt. %, based upon the total amount of monomer to be polymerized therewith.
The preferred olefin and diolefin monomers that are used to prepare the polyolefin backbone of the present styrenic-group-terminated polyolefins include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 3-methyl-1-butene, 4-methyl-1-pentene, cyclopentene, norbomene, phenylnorbornene, indanylnorbomene, 1,4-hexadiene, 1,5-hexadiene, and vinylidenenorborene. These monomers can be used either singly or as a combination of two or more monomers. The resulting polyolefin stereo-structure can be anyone of the five types of tacticity known for polyolefins, namely: atactic, syndiotactic, isotactic, hemiisotactic and isotactic stereoblock, which are very much controlled by the catalyst used.
The styrenic chain transfer agents contemplated for use in the present invention include styrene and styrene derivatives containing a substituent that is stable to the active site under the polymerization conditions. The styrenic chain transfer agents may be illustrated by the following structural formula: 
wherein n is from 0 to about 6, and most preferably from 0 to about 3, and Xxe2x80x2 is a group selected from H, Cl, Br, I, COOR, Oxe2x80x94BR2, Oxe2x80x94SiR3, N(SiR3)2, BR2, SiR3 (where R is a C1 to C10 linear, branched or cyclic aliphatic alkyl group or aromatic alkyl group) and CHxe2x95x90CH2.
The polymerization reaction may be carried out under the conditions similar to those in conventional metallocene polymerizations. In particular, the polymerization may be carried out under batch conditions, such as in an inert gas atmosphere and the substantial absence of moisture. Preferably the polymerization is carried out continuously in a typical continuous polymerization process with inlet pipes for monomers, catalysts and diluents, temperature sensing means and an effluent overflow to a holding drum or quench tank. In solution and dispersion polymerization processes where an inert diluent is used, a hydrocarbon solvent such as hexane, heptalne, cyclohexanie, toluene, xylene, or the like, can be used. The polymerization temperature for such processes typically would range from about 10 to 800xc2x0 C., preferably from about 25 to 70xc2x0 C. The overall residence time can vary, depending upon, e. g., catalyst activity and concentration, monomer concentration, reaction temperature, monomer conversion and desired molecular weight, and generally will be between about thirty minutes and five hours, and preferably between about 1 and 2 hours. Typically, the resulting styrenic unit-terminated polyolefins would be weighed and subjected to NMR, DSC and GPC analysis to determine their polymer structure, thermal transition temperature, molecular weight, and molecular weight distribution, respectively.
One major objective of this invention is to prepare polyolefin having a terminal functional group that can serve as a reactive site for coupling reactions or as an initiator for polymerization processes that produce polyolefin diblock copolymers. Some of the protected functional end groups, such as COOR, Oxe2x80x94SiR3 and N(SiR3)2, used during the polymerization can be de-protected by HCl to recover COOH, OH and NH2 terminal group, respectively. On the other hand, the benzylic alkyl or alkenyl groups, such as "PHgr"-CH3 and "PHgr"-CHxe2x95x90CH2, respectively, are very reactive in many chemical reactions, including free radical, cationic and anionic processes [see U.S. Pat. Nos. 5,543,484; 5,866,659; 6,015,862; and 6,096,849]. For example, both groups can be metallated easily with butyl lithium to form a benzylic anion at the polyolefin chain end, which can then carry out living anionic polymerization of styrene and methyl methacrylate to produce polyolefin diblock copolymers. Overall, the subsequent derivatization reactions widely broaden the polyolefin composition and structures.